1. Field of the Invention
The present invention relates to a flow control device of an engine.
2. Description of the Related Art
Up until now, use has been made of an exhaust gas recirculation (EGR) device comprised of an EGR passage connecting the exhaust passage of an engine and the intake passage of an engine and an EGR control valve disposed in the EGR passage. In this EGR device, the amount of the EGR gas which is made to recirculate in the engine intake passage is controlled by the EGR control valve so that the EGR rate (amount of EGR gas/(amount of EGR gas+amount of intake air)) becomes the target EGR rate.
The pressure in the EGR passage, however, pulses due to the effect of the pulsation of the exhaust caused in the exhaust passage of the engine. If the pressure in the EGR passage pulsates in this way, the EGR rate will fluctuate causing the combustion to fluctuate as well.
Therefore, to suppress the pulsation of the pressure in the EGR passage, an EGR device which provides the EGR passage with an expanded chamber and throttling portion has been known (see Japanese Unexamined Utility Model Publication (Kokai) No. 63-10255).
On the other hand, the EGR control valve is usually comprised of a valve body disposed in the EGR passage, a diaphragm connected to the valve body, and a pressure control chamber defined by the diaphragm. By controlling the magnitude of the negative pressure in the pressure control chamber, the amount of the EGR gas is controlled. With this EGR control valve, when the pressure in the EGR passage pulsates, the valve body and the diaphragm will vibrate. The amplitude of the vibration of the valve body and the diaphragm becomes largest at a specific engine speed as will be explained later. If the valve body and the diaphragm vibrate strongly in this way, however, the durability of the EGR control valve will fall.
On the other hand, if the pulsation of the pressure in the EGR valve is suppressed such as in the above known EGR device, it is considered that it is possible to suppress even the vibration of the valve body and the diaphragm of the EGR control valve. The more one tries to suppress the pulsation of the pressure in the EGR passage, however, the harder it becomes for the EGR gas to flow, so the pulsation of the pressure in the EGR passage cannot be suppressed that much. Therefore, with the method of suppressing the pulsation of the pressure in the EGR passage as in the above known EGR device, therefore, there is the problem that it is not possible to sufficiently suppress the vibration of the valve body and the diaphragm of the EGR control valve.